1. Field of the Invention
This invention relates to providing video services to hybrid fiber optic/coaxial cable (HFC) networks and, more particularly, to providing multi-channel compressed digital video to mini-fiber node (mFN) HFC networks.
2. Background of Related Art
Conventional CATV systems provide downstream broadcast information from a central office (CO) to end-units (EUs) for multiple CATV channels (AM-VSB) using analog broadcast signals from 55 MHz to 350 MHz, 550 MHz or even 750 MHz. Cable operators have incentives to increase the channel capacity of their coaxial cable systems to thereby provide additional services such as premium and pay-per view channels, which increase revenue. However, upgrading conventional coaxial cable or hybrid fiber optic/cable (HFC) systems to 750 MHz (or from 350 MHz to 550 MHz) requires re-engineering the entire cable plant including at least amplifier replacement (upgrade) and associated amplifier spacing. Further, many conventional system operators also want to provide broadcast digital signals, as well as broadcast analog signals over a single transmission line. However, this is difficult, as impulse noise caused by the analog signals can cause errors in the digital signals. See, for example, Lu et al., Clipping Induced Impulse Noise and Its Effects on Bit-Error Performance in AM-VSB/QAM Hybrid Lightwave Systems, PTL July 94, pp. 866-868, which is herein incorporated by reference. The expense of such cable plant upgrades explains why the majority of all CATV plants in the U.S. have not been conventionally upgraded to 750 MHz.
U.S. patent application Ser. No. 08/526,736 filed Sep. 12, 1995, the subject matter of which is incorporated herein by reference, provides an alternative mFN upgrade to an HFC network. The pre-existing HFC network provides a first access path from the CO to the EUs. In the resulting mFN-HFC networks, the mFNs receive signals from a central office (CO) through a second access path separate from the preexisting HFC network for transmission to EUs. Further, the mFNs can receive upstream signals from the EUs for transmission back to the CO over the second access path. In addition, conventional wisdom, as exemplified by Stoneback et al., Designing the Return System for Full Digital Services, Society of Telecommunications Engineers, Jan. 10, 1996, pages 269-277, the subject matter of which is incorporated herein by reference, suggests a constant power/Hz as the preferred allocation of power/Hz when many different signal types including various modulation schemes of differing bandwidth are carried. However, problems including mFN-HFC network inefficiencies result by not allocating power/Hz based on the services provided by each signal type and the performance requirements of each provided service.
Thus, an efficient, cost-effective apparatus and method is needed to upgrade existing CATV systems to provide compressed digital video (CDV) for broadcast television channels and improve power allocation over a mFN-HFC network.